It has long been known in the industry to subject a nonwoven web, normally made by depositing filaments on a belt, to a setting process. For nonwovens with masses per unit area of from 10 to 80 g/m2, the deposited layer, web, or mat is as a rule consolidated by means of a thermocalender. This produces thin nonwovens with good strength. Heavier and more voluminous filament mats are more difficult to consolidate since it is very difficult to penetrate to the center of the mat with enough heat to do the compacting and entangling wanted for good consolidation. If the heat is applied long enough to melt the filaments of the core region where they touch and intersect, the surface is overcooked and melted.
If heavier and more voluminous nonwovens are to be manufactured, other consolidation methods are used, in particular mechanical needling and hydraulic needling with intense water jets or thermoconsolidation using hot air. With these consolidation methods, it is always necessary to separate the mat from the belt or sieve belt and to deliver it to the consolidation/final consolidation with as little damage as possible to the mat and without harming the uniformity of the mat.
US 2005/0077012 discloses using water jets to consolidate the filament mat immediately downstream of where it was deposited, in fact without the interposition of a heated outfeed roll. This should prevent particles or droplets from the outfeed roll from being rolled into a deposition sieve belt and thus reducing the service life of the deposition sieve belt. This system has the disadvantage that the direct consolidation of the loosely laid filament mat by means of water jets can cause unwanted irregularities. The loosely laid filament mat must therefore be secured against slippage in a particularly complex fashion.
In the context of the present invention, the term “filaments” normally refers to so-called endless filaments. Due to their quasi-endless lengths, endless filaments differ from staple fibers, that are normally considered to have significantly shorter lengths of 10 to 60 mm, for example.